The present concept on the contraction mechanism of cardiac muscle indicates that the intracellular free Ca ion concentration at the time of excitation determines the strength of cardiac muscle contraction. Evidence suggests that Ca ion moves into the cardiac cell during excitation. Since the amount of Ca ion entered during excitation must be transported against the electrochemical gradient out of the cell during relaxation, this suggests the presence of an active transport mechanism for Ca ion in cardiac muscle membrane. No experimental basis for this Ca ion pump has been demonstrated in heart muscle. However, in the red cell membrane the presence of a Ca ion pump has been established. An attempt will be made to demonstrate the presence of a similar active Ca ion transport in the heart muscle cell membrane. For this purpose, further characterization of the Ca ion pump in the red cell membrane will be made with regard to the relationship between the active transport and Ca ion-activated ATPase. Since the cell membrane also contains Na-K ion activated ATPase, the relationship between Na-K ions ATPases and Ca ion ATPase will be investigated to understand the interaction of the sodium pump and the calcium pump. The results obtained in this study will be applied to the heart muscle cell membrane preparation.